The present invention relates to methods and apparatus for ensuring that a route generated by a vehicle navigation system may be safely navigated by the user. More specifically, the present invention provides a vehicle navigation system which generates routes which are less likely to include consecutive maneuvers which are difficult and/or hazardous to execute.
Currently available vehicle navigation systems typically generate routes using variations of well known search algorithms in conjunction with commercially available map databases. Some algorithms attempt to generate optimum routes, i.e., shortest distance or shortest travel time, using a variety of techniques. Unfortunately, while these algorithms typically generate routes which obey travel restrictions, e.g., one-way streets, and avoid prohibited maneuvers, they do not typically determine whether a maneuver is difficult to execute before including it in the generated route. FIGS. 1-5 show several examples of troublesome consecutive maneuvers.
In FIG. 1, route 100 includes a right turn from road 102 to road 104, followed by a left turn onto road 106. The first maneuver, the right turn, places the vehicle in the far right lane of road 104 which is a four-lane, one-way road. The left turn onto road 106 is less than 200 feet down the road from the intersection of roads 102 and 104, and must be executed from the far left lane of road 104. While these consecutive maneuvers are theoretically possible, the second maneuver, i.e., the left turn, is extremely difficult and potentially hazardous because so many lanes of traffic must be crossed in such a short distance. The situation becomes even more hazardous where, as is often the case, the user is relying heavily on the generated route because she is not familiar with the area.
FIG. 2 shows a similar situation except that road 204 is a two-way road. In this situation, the danger arises from entering the stream of traffic on road 204 from road 202, and stopping abruptly within a short distance for the purpose of making the required left turn onto road 206. FIGS. 3 and 4 show situations similar to FIGS. 1 and 2 except that the first maneuver is a left turn and the second is a right turn. FIG. 5 shows a situation in which the first maneuver involves exiting the westbound section of a freeway 502 and a second maneuver which is a left turn onto road 504 across oncoming traffic which is entering freeway 502. The difficulty and danger associated with such a scenario is self evident.
In view of the foregoing discussion, it is apparent that some means for reducing the incidence of difficult and/or dangerous consecutive maneuvers in a generated route is desirable.